linux-kernel - Re: [PATCH] char: misc: Make the code for allocating minor in misc

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Message-ID: <20250910014421.2837-1-zhangjiao2@cmss.chinamobile.com>
Date: Wed, 10 Sep 2025 09:44:20 +0800
From: zhangjiao2 <zhangjiao2@...s.chinamobile.com>
To: gregkh@...uxfoundation.org
Cc: arnd@...db.de,
	linux-kernel@...r.kernel.org,
	zhangjiao2@...s.chinamobile.com
Subject: Re: [PATCH] char: misc: Make the code for allocating minor in misc_register more concise

>> On Tue, Sep 09, 2025 at 04:58:35PM +0800, zhangjiao2 wrote:
>> From: zhang jiao <zhangjiao2@...s.chinamobile.com>
>>
>> There is no need to check the registered misc dev in misc_list.
>> If misc_minor_alloc failed, it meens the minor is already alloced
>> and the misc dev is linked in misc_list.
>>
>> Signed-off-by: zhang jiao <zhangjiao2@...s.chinamobile.com>
>> ---
>>  drivers/char/misc.c | 32 +++++++-------------------------
>>  1 file changed, 7 insertions(+), 25 deletions(-)
>>
>> diff --git a/drivers/char/misc.c b/drivers/char/misc.c
>> index a0aae0fc7926..fc2f5e8b2f95 100644
>> --- a/drivers/char/misc.c
>> +++ b/drivers/char/misc.c
>> @@ -211,6 +211,7 @@ int misc_register(struct miscdevice *misc)
>>  	dev_t dev;
>>  	int err = 0;
>>  	bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
>> +	int minor = 0;
>>
>>  	if (misc->minor > MISC_DYNAMIC_MINOR) {
>>  		pr_err("Invalid fixed minor %d for miscdevice '%s'\n",
>> @@ -221,32 +222,13 @@ int misc_register(struct miscdevice *misc)
>>  	INIT_LIST_HEAD(&misc->list);
>>
>>  	mutex_lock(&misc_mtx);
>> -
>> -	if (is_dynamic) {
>> -		int i = misc_minor_alloc(misc->minor);
>> -
>> -		if (i < 0) {
>> -			err = -EBUSY;
>> -			goto out;
>> -		}
>> -		misc->minor = i;
>> -	} else {
>> -		struct miscdevice *c;
>> -		int i;
>> -
>> -		list_for_each_entry(c, &misc_list, list) {
>> -			if (c->minor == misc->minor) {
>> -				err = -EBUSY;
>> -				goto out;
>> -			}
>> -		}
>> -
>> -		i = misc_minor_alloc(misc->minor);
>> -		if (i < 0) {
>> -			err = -EBUSY;
>> -			goto out;
>> -		}
>> +	minor = misc_minor_alloc(misc->minor);
>> +	if (minor < 0) {
>> +		err = -EBUSY;
>> +		goto out;
>>  	}
>> +	if (is_dynamic)
>> +		misc->minor = minor;
>>
>>  	dev = MKDEV(MISC_MAJOR, misc->minor);
>>

> Does this pass the new test suite for the misc code allocation logic
> that we now have in the tree?  Or do we need to write a new test-case
> for this codepath?

 I didn't take this new test suite, can you do it for me? I don't think there's 
 a need to write a new test-case for this codepath. 

thanks,

zhang jiao